Config on RB750

Hi guys

Let me start to honestly say how exceptionally impressed I am with the product - I have been playing with it a bit basically going through the menu’s and am blown away with the capabilities and nice-to-have’s that is available in such a well priced device.

This has sparked the idea to replace all our load-balance and failover links with this product; this is where I ran into some problems.

This is my very first interaction with the product and I have not had any training whatsoever on the OS, so please forgive me if some questions are typical noob stuff.

The problem:
Being in greater Africa, we suffer from congested exchanges and chronic line breaks etc.

The current solution:
For our company I have signed up for three separate and independent ISP’s to be able to fail over to another ISP should the one go down.
Each provider has it’s own gateway, the 1Mb fibre line runs into a CentOS machine, the one dsl provider into a D-Link load balancer and the other DSL provider into a ClearOS system for load balancing.

Currently I have to fail over manually and update DNS and mail relay hosts on the necessary machines.

The dream:
The fibre line would use a RB750 as purely a VPN gateway, so I can use that with the default configuration.

It would be great if I can run one RB750 per dsl provider (thus 2 RB750 establishing the connection) - thus having 2 or 3 ports assigned to PPPoE and one to LAN.
Then have one more RB750 providing the fail-over between the two providers as well as redirecting all SMTP and DNS traffic. SMTP to a specified smarthost and DNS to the automatically obtained forwarder.

This will enable me to configure all the clients to access the ‘front’ 750 and that 750 handles all the issues.

The sales person assured me that more than one WAN port can be configured on the device, but I fail to find where I can assign more. Establishing the connection seems possible to do via the web config, but the firewall setting only provides me with one port labeled WAN.

I guess the first step would be to figure out how to assign three ports to WAN and load-balance over them. (Is the load-balancer packet based or session based out of interest?)

Embarrassing, but the default places port1 as WAN and 2-5 as internal, and I am also not able to figure out how to ‘move’ the internal port to either 1 or 5 - just to alleviate confusion with cabling it would be nice to have all the WAN ports either as 1-3 or 3-5 (preferred).

Any pointers or help will be greatly appreciated.
Thanks very much in advance!

Just to add - the third device will come later, so if the redirects can happen on the ‘outside’ devices it would also work great, almost like creating a transparent DNS and SMTP proxy.
The actual fail-over I can still do manually to start - as failure is often not total, but for example only international connectivity.